Secondary vacuum system



Dec. 26, 1933. L, R, AY ET AL 1,940,857

SECONDARY VACUUM SYSTEM Filed March 24, 1931 iNVENTORS.

ATTORNEY Patented Dec. 26, 1933 PATENT; OFFI SECONDARY VACUUM SYSTEM Lawrence R. Golladay Wilkinsburg, and Charles H. Hodgkins, Pittsburgh, Pa.," assignors to. Westinghouse Electric and Manufacturing Company, a corporation of Pennsylvania Application March .24, -1931. .Serial No. 524,868 7 Claims. 01. 230- 29) Our invention relates to a secondary vacuum system and particularly to an oil-sealed-pump and valve for a vapor electric device;

In the use of mercury-arc rectifiers,-it has been, customary to maintain the operative vacuum of the-device by constantly pumping to eliminate any gas that might leak into,- or be evolved in, I

the rectifier. The'rectifier tank properly is preferably pumped by a mercury-vapor pump which will work satisfactorily only against a back pressure of a few millimeters of mercury. Consequently, it is necessary to use a secondary vacuum system capable of discharging the. pumped gases against atmospheric pressure. Originally, it"was .necessary to run both the vapor pump and the secondary pump continuously in order to-free the device'of vapor.

Since the mechanical pump was subject'to Wear, this continuous operation proved uneconomical and, eventually, an'interstage reservoir, as shown in Patent No. 1,716,160, was introduced between the" vapor pump and the fmechanical pump, and suitable pressure switches were pro vided,.so that the secondary or mechanical pump was only used a small fraction of the time that the rectifier was in operation.

The mechanical or secondary pumps are neeessarily provided with suflicient clearance to allow mechanical movement of the parts. Consequently, when the pump was not in operation; it was mechanically almost impossible to prevent leakage through it. To prevent this leakage from reaching the rectifier, it is necessary to provide a vacuum ti'ght' valve between the secondary pump and the interstagere'servoir. These valves have been veryeexpensive to construct and their operation and maintenance required the services of one-skilled in the handling of them.

Wehave discovered that the ordinary mushroom or poppet-type valve, while incapable of maintaining a ,vacuum ti'ght seal, when dry, will when oil sealed, maintain vacuum-tightness in'- definitely. We have further found that the oil-Q poppet-type valve for maintaining a substantially perfect vacuum seal for the secondary system.

The poppet valve is provided with. a magnetic opening device'which'is energized by a speed responsive switch which is so set that thepoppet valve will not open until the rotary oil-sealed pump is operating at pumping-speed. This insures that the secondary valve will be open only when the pump is operative and will prevent any possibility of leakage through the secondary system.

Other objects and advantages of our invention will be apparent from the following detailed description, takeninconjunction with the accompanying drawing-inwhich p I Figure 1 is aview, partly in elevation and partly in section, of the essential elements of our secondary system, and Fig. 2 isa schematic diagram of our'system,

The apparatus disclosed in the drawing comprises a mechanical pump, such as the vertically mounted rotary-vanepump i immersed ina reservoir 2 filled with oil. The pump '1 is directly connected to a driving motor 3 on the shaft 5 of which is mounted-a centrifugal or speed-responv sive switch 7 for controlling the vacuum valve presently to be described.

The rotary pump is provided with a discharge passage or conduit 9 in which is mounted a so that, when the pump is operating, it discharges directly to atmosphere without interference by the" oil surrounding the pump. The; discharge duct '9 is provided with a comparatively small vent l1 communicating withfthe oil in thereservoir' 2' sothatpwhen the dischm'geprfessure of the pumpis reduced, the discharge conduit will be flooded'with oil to from the pump.

The pump is further provided with an inlet passage 15 adapted'to be connected'to a vessel (not shown) intended to be evacuated, such as exclude the atmosphere the inter'stage reservoir of a vapor electric device.

,Since. the oilsealed pump is operated only in termittently, a vacuum valve is placed in the inlet passage '15 The body 16 of the valve is provided with a plurality 'ofpassages, one' of which 1'7 communicates with the interstage reservoir and another 13 with the pump inlet passage. Still another 19 is provided through which extends the stem 20 of'an operating tappet for the valveelement. A removable valve seat 24 is located in the valve body 16, said valve seat being provided with a substantially central opening 25 and a valve-stem guide 26. A mushroom for the same.

or poppet valve 28 extends through the valve seat and is supported by the stem guide 26. A spring member 29 is provided for maintaining'the mushroom valve 28 in substantially vacuum-tight contact with the valve seat.

The portion of the valve tappet extending beyond the casing is enclosed in a vacuum-tight metallic bellows 30 which is provided with a contact element 32 for, operating the valve stem.

The valve-actuating mechanism comprises an operating lever 34 pivoted on the valve body adjacent to the extending tappet and having a portion 35 adapted for contact with the tappet. A second lever 36, pivoted on the valve body, has resilient driving contact 38 therewith so that the two levers, combined, act substantially as a bell crank for actuating the valve stem. The composite bell crank is actuated. by an electromagnet ii) having a movable armature 41 pivoted to the outer end of the actuating lever 36. The electromagnet is controlled by the speed-responsive switch '7 mounted on the pump shaft. In operation, the pump is started by pressure-responsive switches in the chamber to be evacuated (not shown). As soon as the pump has reached pumping speed, the centrifugal switch 7 energizes the valve-operating magnet 40 which, through itsbell-crank assembly, compresses the valve spring 29 to open the valve to permit evacuation of the chamber by the rotary pump.

The pump discharges, through the exhaust conduit, to an open space in the oil reservoir surrounding the pump from which it is vented to atmosphere by the vent 45 in the top of the reservoir.

When the pump is operating, it will force the excess oil out of the pump and out of the exhaust passage, so that there is very little hindrance by the presence of the oil. However, when the exhaust pump discharge pressure falls, oil from the reservoir will pass through the connection into the exhaust conduit, and, leaking past the check valve, will flood the pump proper, and leaking into the pump inlet passage will reach the poppet valve and provide an oil seal Upon resuming operation, the pump will first expel the oil contained therein but will leave a film of oil on all the working parts of the pump, so that an effective oil seal will be maintained at all times.

While we have shown and described a specific embodiment of our invention, it is apparent that changes and modifications could be made therein without departing from the spirit and scope of our invention. We desire, therefore, that only such restrictions shall be imposed as are included in the appended claims or such as may be necessitated by the prior art.

We claim as our invention:

1. A secondary vacuum system for a vaporelectric device comprising a rotary oil-sealed pump, a discharge vent for discharging the pumped fluid to atmosphere, a check valve in said vent, an oil reservoir adjacent to said pump, a connection between said reservoir and said vent for admitting oil thereto, said connection being of less capacity than the vent, an inlet passage for connecting the pump to a vessel to be evacuated, a valve seat in said passage, a poppet valve for closing said passage, means for normally holding said valve in closed position, and magnetic means for opening said valve.

2. In combination, an oil-sealed mechanical vacuum pump, an oil reservoir, an exhaust for said pump extending through said reservoir, means for supplying oil to said pump from said reservoir, an inlet conduit for the pump, said inlet being. adapted for connection to a vessel to be evacuated, and a spring-seated poppet valve for closing said inlet, said valve being sealed by oil leaking through said pump.

3. In combination, an oil-sealed mechanical vacuum pump, an oil reservoir surrounding said pump, an exhaust for said pump extending through the oil, means for supplying oil to said pump from said reservoir, an inlet conduit for the pump, said inlet being adapted for connection to avessel to be evacuated, a poppet valve for closing said inlet, said valve being sealed by oil leaking through said pump, magnetic means for opening said poppet valve, and a centrifugal switch for energizing said magnetic means at a predetermined pump speed.

l. In a vacuum pumping system, a rotary oilsealed pump, an inlet passage for said pump, a

vacuum valve in said passage comprising avalve casing, a seat therein, a mushroom valve element adapted to cooperate with said seat for closing said passage, the stem of said valve elementex tending outside or" the valve, a metallic bellows for sealing the stem and magnetic means for actuating the valve element.

5. A vacuum system comprising an oil-sealed rotary pump, a discharge for said pump, a check valve in said discharge for decreasing backpressure on the pump, and an oil reservoir surrounding thepump, said discharge having a vent for supplying oil for sealing the pump, an inlet pas' sage for said pump adapted for connection to a vertically disposed rotary pump, an oil reservoir enclosing said pump, a discharge conduit extending above the normal oil level in said reservoir,

said conduit having a vent for admitting oil from said reservoir to said conduit and a check valve between the conduit and the pump.-

7. A secondary vacuum system comprising a vertically disposed rotary pump, an oil. reservoir enclosing'said pump, a discharge conduit-extending above the normal oil level insaid reservoir, said conduit having a vent for admitting oil from said reservoir to said conduit and a check valve between the conduit and the pump, an inlet con duit for said pump, a poppet valve in said conduitand magnetic means for opening said poppet valve. I

LAWRENCE R... GOLLADAY. CHARLES H. I-IODGKINS.

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